A nickel-metal hydride storage battery, nickel-cadmium storage battery, nickel-zinc storage battery, and the like, have been used as alkaline storage batteries. The nickel-metal hydride storage battery that has a high output and is environmentally safe is especially widely used as an electric source for electric vehicles, hybrid electric vehicles, electric bicycles, power tools, and the like.
A nickel-metal hydride storage battery uses nickel hydroxide for a positive electrode and a hydrogen absorbing alloy for a negative electrode.
There is a problem in a nickel-metal hydride storage battery that when the battery is repeatedly charged and discharged, the hydrogen absorbing alloy used for the negative electrode is deteriorated by oxidation, which is caused by oxygen generated at the positive electrode during overcharge, and gradually the discharge capacity of the battery is reduced and charge-discharge characteristics are deteriorated. There is also a problem that the release of hydrogen from the hydrogen absorbing alloy in which hydrogen is absorbed becomes slow when the nickel-metal hydride storage battery is used at a low temperature and deteriorates discharge characteristics at the low temperature.
An alkaline storage battery with improved charge-discharge cycle characteristics has been proposed that is provided by the addition of yttrium or a yttrium compound to a negative electrode containing a hydrogen absorbing alloy (as disclosed in Japanese patent Laid-open publication (Tokkai) No. Hei 6-215765) to prevent oxidation of the hydrogen absorbing alloy used for the negative electrode that is caused by oxygen generated from the positive electrode during overcharge.
However, even such an improved alkaline storage battery in which yttrium or a yttrium compound is added to the hydrogen absorbing alloy used for the negative electrode cannot exhibit sufficiently improved charge-discharge cycle characteristics. Discharge characteristics at a low temperature are also not sufficiently improved.